This invention relates to an apparatus for cutting and stripping insulation from an electrical conductor, and more particularly, to a blade for cutting insulation from electrical wire of various sizes.
The conventional wire cutting and stripping machine includes a cutting head that consists of a pair of cooperating cutting blades and two pair of cooperating stripping blades, one pair of which is located upstream of the cutting blades and the other pair is located downstream of the cutting blades. After the insulated wire or conductor is fed to the cutting head, the cutting blades operate to sever the insulated conductor and provide a cut length, while the stripping blades act to merely cut the insulation. With the stripping blades still closed, the insulated conductor is pulled in an upstream direction and the cut length is pulled in a downstream direction, thereby pulling a slug of insulation from both the conductor and the cut length.
There are four basic types of blades for high production stripping of insulation from insulated electrical conductors, the die type or butt style, the V blade with a base radius, the V blade with a 90.degree. angle and little or no radius in the base, and the compound angle blade. Each cutting blade is designed to cut the insulation without nicking or scoring the conductor. A nick in the conductor decreases the conductor's electrical current carrying capacity so as to produce stress concentrations in the conductor. Strength concentrations in the conductor decrease the conductor's tensile strength. In the die type or butt style design, a pair of knife blades form two halves of a through hole. The two blades are closed over the .insulation of a specifically sized insulated conductor at the desired location thereon. The through hole is designed to closely conform to the configuration of the conductor. This hole controls the depth of the cut and prevents nicking and scoring of the conductor.
While the die type blade adequately cuts the insulation about a specifically sized insulated conductor, the die type or butt style blade suffers from three disadvantages. First, a pair of die type blades may be used only with one size of insulated conductor. If the blades are used on a different size wire, the insulation may not be completely cut or the blades may nick and score the conductor.
Second, squeezing of the insulation between the conductor and the blades may prevent the blades from fully closing onto the conductor. As a result, the portion of the insulation which is not completely cut through to the conductor must be torn from the parent insulation. The physical characteristics of some insulation material makes it difficult to tear, so it is desirable to minimize the uncut portion of the insulation.
Third, die type or butt style blades have a low tolerance for accommodating off center insulated conductors transported between the open blades. In many applications, special wire guides in the form of mechanical fingers are required to insure the insulated conductor is on the center line of the closed blades.
A V blade with a base radius is manufactured with a sharp edge cutting radius at the base of the V for slicing through the insulation. While more versatile than the die type blade, the V blade with a base radius is limited to only a slight range in wire size. Because of the V-angle, the cutting radii may not form a full circle around the conductor when the blades are closed. As a result, a portion of the insulation remains uncut and must be torn from the parent insulation during the stripping operation.
The V blade with a 90.degree. angle and little or no radius in the base is the most universal of the basic types of cutting blades. As with the V blade with a base radius, the V blade with a 90.degree. angle does not form a full circle around the conductor when the blades are closed. However, for smaller size wires, the portion of the insulation which remains uncut is insignificant. However, in larger sizes of wire, a large portion of insulation remains uncut. As previously described, tearing a substantial portion of the insulation from the parent insulation during the stripping operation is undesirable.
The compound angle blade is illustrated in U.S. Pat. No. 4,577,405 to Butler. The compound angle blade is designed to gather greatly offset insulated conductors while increasing the circumferential contact between the blades and the conductor. The blade is designed with a pair of angled paths or openings leading to a radiused cutting edge. While the compound angle blade shown in the Butler patent is adequate for slight variations in wire size, the compound angle blade suffers from the same inadequacies as the other basic types of cutting blades. When there is a large range of wire sizes, a significant portion of insulation may remain uncut or the conductor may be nicked.
Therefore, it is a primary object and feature of this invention to provide a blade for cutting insulation from an insulated electrical conductor wherein the blade is capable of cutting a substantial portion of the insulation about the conductor without nicking or scoring the conductor.
It is a further object and feature of the present invention to provide a blade for cutting insulation from an insulated electrical conductor wherein the blade design minimizes the amount of insulation which remains uncut.
It is a still further object and feature of the present invention to provide a blade for cutting a substantial portion of the insulation about various size electrical insulated conductors.